Method of manufacture of an aluminum alloy, and the alloy obtained by this process



Nov. 28, 1961 J. HERENGUEL ET AL 3,010,824

METHOD OF MANUFACTURE OF AN ALUMINUM ALLOY, AND THE ALLOY OBTAINED BY THIS PROCESS 2 Sheets-Sheet 1 Filed Oct. 8, i958 INVENTORS Jalb fiimrazzyuez Pierre Zelimg Zua'az 63ml! BY Henri florz'ou Nov. 28, 1961 J. HERENGUEL ET AL METHOD OF MANUFACTURE OF AN ALUMINUM ALLOY, AND THE ALLOY OBTAINED BY THIS PROCESS Filed Oct. 8, 1958 2 Sheets-Sheet 2 INVENTORS Jan [kzzre Hare lelozqy Zwl'en 61% BY .Hrlzrl' 0011'010 ATTORNEYS Unite States Patent 3,010,824 METHOD OF MANUFACTURE OF AN ALUMINUM ALLOY, AND THE ALLOY OBTAINED BY THIS PROCESS Jean Herenguel, Versailles, Pierre Lelong, Verrieres-le- Buisson, Lucien Grail, Paris, and Henri Coriou, Plessis Robinson, France, assignors to-Etablissement Public: Commissariat a lEnergie Atomique, Paris, France Filed Oct. 8, 1958, Ser. No. 766,069 Claims priority, application France Oct. 8, 1957 8 Claims. (Cl. 75-138) In order to obtain aluminum alloys which are resistant to water under pressure and at high temperatures, various authors have studied alloys of aluminum-iron-nickel. Mention must be made especially of Draley and Ruther, Carlsen, Dillon, Wilson and Troutner.

These various authors have studied alloys having a content in each one of the two added elements ranging from 0.2% to 2%. In all cases the alloys were obtained by smelting processes and were studied in that condition. Their structure is described as being formed of a network of constituents in separate phases, which surround the coarse granules of melt formed by solid solution which is nearly homogeneous.

The behaviour in water at high temperature of an alloy having a certain percentage composition depends on the even distribution of the added elements, and in particular, in the case of the insoluble ones, on the fineness of their dispersion, as separate phases, in the matrix formed by the solid solution.

It is thus essential to ensure the finest possible dispersion of these constituents in the structure which is exposed to attack, or at least to ensure by a controlled operation, the size of the pattern of distribution.

A known process for ensuring a fine distribution consists in bringing about this fine distribution in the course of the solidifying of the rough castings which will be used for the manufacture of the finished pieces. This can be done by solidifying quicklyor by the addition of elements which favour this fine distribution (for example titanium). But these procedures have a limited eifeot, notably when applied to ingots of the usual industrial size (for example of a diameter exceeding 200 mm. or a thickness exceeding 100 mm).

The subject of the present invention is a method of manufacture of an alloy of aluminum and at least one of the metals, iron and nickel, which alloy is resistant to water under pressure and at high temperature. It also deals with the alloy obtained by this process.

The process according to the invention is distinguished in that granules are formed of an alloy of aluminum and the added metal, the latter having a content in each granule of between 0.05 and 4%, that these granules are compressed while hot and extruded, and that in the course of the extrusion shearing is produced in the alloy.

In the particular instance where semi-finished articles of alloys produced according to the invention are exposed to corrosion only at their surfaces, it is sufficient to obtain the structure produced by the shearing action as a coating or skin of sufiicient thickness on these semifinished products. This is the case with metal sheets or bars, the mounting and use of which would not bring either their core or cut surface in contact with a corrosive medium. This coating should have preferably a thickness of at least 1 mm. at the time of use to allow for any possible loss of thickness due to finishing operations such as planing and polishing.

The advantages of the alloys obtained according to the invention are as follows:

The ability to resist the action of water at 350 C. under a pressure of 160 kg./cm. in such a way that after 5,000 hours of contact, no deterioration is perceptible;

The ability, owing to the low nickel content, to resist adequately corrosion by cold water. This is a point of great practical importance, since the apparatuses working at high temperature must also be able to withstand, without disadvantage, contact with cold water during periods of inactivity. A high nickel content would cause a considerable corrosion in the cold, by pitting of these alloys on contact with water; I

The ability to avoid any localized corrosion because of the very homogeneous structure at the surface arising from the very uniform distribution of the protective constituents which are present in separate phases.

The alloys should have as small a silicon content as possible, and preferably smaller than 0.01%. The content of each one of the main impurities, zinc, magnesium, manganese, should preferably be lower than 0.005%, and that of copper preferably lower than 0.01%.

Furthermore, the fineness of the distribution of the constituents in separate phases is one of the main characteristics of these alloys. In order to achieve this in the finished or semi-finished products it is necessary for the starting products, which are further used in the preparation of the present alloys, to have, themselves, a relatively fine distribution.

For this purpose, the granulated metal can be obtained by the spraying and rapid solidifying of a molten alloy having the required percentage composition.

The solidifying of each drop of alloy is sufficiently rapid for the distribution of the constituents in separate phases to be very fine, and of a smaller pattern than that of the particles forming the granules. By regulating the conditions of the spraying and by sifting the granules to a definite granular size, a distribution of the constituents in separate phases is ensured, according to a size pattern which is lower than a pre-set limit.

The granules can also be obtained starting with granules of aluminum (of tested purity) which are spherical or better still laminar, each granule being coated by the added metal. This coating can be effected chemically, the previously sifted aluminum granules, spherical or laminar, being treated by a chemical process, for example cementa-tion, thus ensuring the deposit on their surface of a sheath of the added metal, or of a compound of this metal, which can be alloyed with aluminum, either directly in the case of the metal itself, or after reduction in the case of the compound, thus forming an alloy having the required relatively fine phase distribution. The alloying of the granules or lamellae of aluminum thus coated by chemical means is effected by drying them and subjecting them to a heat treatment which ensures an intermetallic diffusion, this diifusion being preceded by a reducing action when a compound of the metal to be added has been deposited on the surface of the granules.

The aluminum granules can also be coated mechanically. In that case the metal or metals added are finely disintegrated (with a crusher followed by ball-milling or other suitable means) to a powder of, for example, 1 to 5 1..

The powder so formed is then added to the aluminum granules in a measured quantity in order to obtain the percentage composition required for the final product, and the mixture is placed in a rotating cylinder, with a relatively small quantity of balls. It is then rotated fairly slowly for a time such that all of the added metal powder coats the surface of the aluminum granules.

The aluminum granules can also be coated mechanically with a compound or a mixture of metallic compounds which can be reduced by aluminum.

A heat treatment is undertaken next in order to ensure the reduction as well as the intermetallic diffusion. If the reduction involves evolution of a gas (for example in the case where the compound used is a carbonate or an oxalate), the coated granules or lamellae are subjected to this treatment of reduction and diffusion before the compression while hot. But if the compound used, such as an oxide, does not produce any evolution of gas, this treatment can be undertaken at any stage of the process.

Where the aluminum granules or lamellae are coated by a compound which is capable of reduction by aluminum to give the required added metal, the reduction also produces films of alumina which in turn modify the mechanical properties of the final structure, notably by increasing its limit of elasticity and mechanical resistance, as well as increasing its resistance to deformation by heat, as is well known. It is possible to obtain at the same time, by the process according to the invention, on the one hand an improved behaviour to the action of water at high temperature and a satisfactory behaviour against corro sion at ordinary temperature, and, on the other hand, an improved mechanical behaviour. The size of the aluminum granules or lamellae, taking into account the subsequent alloying and the reduction during alloying, determines the level of the mechanical properties finally achieved.

As has already been mentioned, the granules of alumi num and of the added metal are compressed while hot and later extruded.

It has been found that the transformation by means of extrusion causes an intense shearing in certain regions of the container from which the compacted mass is extruded. This brings about a new distribution of the con stituents which exists in separate phases, which is entirely different from that which exists in a rough solidified casting.

With the usual technique of extrusion, these regions of intense shearing are rather limited, and the structure with a new and fine distribution of the constituents existing in separate phases is limited, in the case of the drawn metal products, to a surface crust which is very thin at the beginning of the metal-drawing, and which increases in thickness as the metal-drawing is continued.

It has been found that similar ingots of an alloy of fixed composition, one having merely been rolled (that is to say not having benefited from the distribution associated with the metal-drawing) and the other having been drawn, do not have the same behaviour in water at high temperature. in the case of the drawn products, the surface is superior in its behaviour to that of the rolled products, but the core of the drawn piece in that respect approximates that of the rolled products.

In the process according to the invention, the distribution of the constituents which exist in separate phases is obtained, as has been mentioned, by the multiplication of the shearing zones in the alloy in the course of the extrusion.

For example, it is possible to efiect, in addition to the shearing taking place in the container of the extrusion apparatus, further shearing in the vicinity of the drawing-plate itself, by causing deviations and constrictions to the outflow ahead of the actual outlet. In this way, the whole of the drawn section will be subjected to the new distribution of the constituents present in separate phases.

By referring to FIGURES 1 to 5 of the drawings, various examples will be described to illustrate the preparation of alloys of aluminum-iron, aluminum-nickel and aluminum-iron-nickel, without thereby limiting the scope of the invention. The arrangements described for carr ing out the processes in connection with these examples are to be considered as forming part of the invention, and it is understood that all similar arrangements can be used equally well within the framework of the present invention.

Examples I to IV relate to processes of preparing of the product of the invention.

Examples V to VII show the influence of metal-drawing on the fineness of distribution.

Example I To liquid aluminum of purity A9 (Si 0.0l%), 1% of iron and 0.1% of nickel are added. The liquid metal is sprayed and cooled to form granules which are sifted to sizes under 300 1. These granules are compressed in the cold at kg./mrn. then at 600 C. at 50 kg./mm. and they are extruded with a drawing ratio of 20. The rough castings are then rolled and brought to a thickness of 1 mm., and they are then reheated.

On the surface of the sheet metal so obtained, as at the core, the thickness of the film attacked is less than 10 after 10 hours in water at 360 C., whereas a sheet metal of the same composition, obtained by the rolling of an ingot solidified by the usual means, shows a film of attack from to 200 under the same conditions of exposure.

Example 11 Aluminum lamellac of purity A5 (Si:0.15%, Fe: 0.30%) of a thickness of 15 to 20 are reheated in air at 350 C. for dcgreasing.

Further, the compound Al Fc is prepared by fusion and then powdered and crushed into particles of l to 3a. This powder is added to the aluminum lamcllac in a quantity sufficient for the total iron content in the mixture to be 1.3%.

7 kilograms of the mixture are placed in a grinder of 700 mm. diameter and of a capacity of 40 litres, together with 70 kg. of steel balls of 10 mm. diameter, rotating at 17 revolutions per minute for 3 hours. The whole of the powdered Al Fe was on the surface of the lamellae.

The coated lamellae were compressed in the cold, then at 620 C., and drawn at 500 C., with a drawing ratio of 20. The rough castings were then rolled to a thickness of 1 mm. and reheated.

After 10 hours in water at 360 C., the depth attacked is about 15 The attacked film is the same, whether the surface or the core of the product was considered.

Samples of the same composition, but obtained by rolling from a rough casting cast by the usual smelting process, showed after 10 hours in water at 360 C., a film of 150 to 20011. with an integranular corrosion.

Under similar conditions, samples of aluminum of purity A5 obtained by rolling a cast ingot or non-coated sintered lamcllae, are completely destroyed.

Example III Identical lamellae to those in Example II are coated with a quantity of powdered CO Fe of a fineness of 2 to 4p. sufficient to ensure that the final iron content should be 1.3%, the coating being effected under exactly the same mechanical conditions as in Example II.

After coating, the lamellae are compressed in the cold at 40 kg./mm. the compressed mass being heated in the air to 620 C. for 3 hours, and then compressed at that temperature and drawn at 500 C. with a drawing ratio of 20.

After rolling to a thickness of 1 mm. and reheating, the samples have the same behaviour to hot water at the surface and core and after 10 hours at 360 C., the uni form film attacked is about 15 Furthermore, the force which must be applied to cause an elongation of less than 0.1% at 300 C., is at least 10 to 20% higher for the rolled samples from the lamellae coated by CO Fe, than for those obtained from the cast ingot of the same composition.

Samples of aluminum of purity A5, under those conditions, are completely destroyed.

Example IV Identical results to the preceding ones are obtained with sintered lamellae which are obtained by coating lamellae of aluminum of a purity of A5 of 15 thickness with 'Fe O in a quantity sufiicient to ensure that the final composition should be 2.3% Fe, with 0.15% Si. The behaviour at the surface and core of the samples is satisfactory, Whereas test-pieces of the same composition obtained by smelting and rolling, are very severely attacked.

Example V This example shows the improvement in distribution brought about by the shearing in the course of drawing.

An alloy of the composition Fe=1% Si 0.01% is solidified in ingots of 100 mm. diameter (in a non-cooled ingot-mould), and subjected to the following treatment:

Drawing at the press at 400 C. Drawing ratio: 25.

The round bar is laminated to 1 mm. thickness, cast in a flat ingot-mould of 5 mm. thickness, it is then rolled while hot and while cold to 1 mm. thickness, and then reheated.

After 10 hours exposure in water at 360 (3., an attack was found as follows:

Uniform and from 4 to 5p. at the surface of the samples emerging from the drawn bar (micrographic section of FIGURE 1).

With local penetrations of 30 to 70 at the core of the earlier samples,

With a penetration of 200p. on the rolled test-pieces which were not drawn (FIG. 2).

Example VI This example shows clearly, with reference to FIGS. 3 and 4, the fineness f the dispersion (FIG. 3) obtained by this invention, and its resistance to corrosion (FIG. 4, a vertical section to that of FIG. 3).

It is an alloy having 1% iron and 0.85% nickel; it has been prepared by known means, by casting, drawing, and rolling. Two zones can be seen side by side, one on either side of the line XX, as follows:

That on the left side shows a sample prepared in accordance with the present invention and shows an improved behaviour in regard to corrosion;

That on the right side which does not have a suflicient dispersion of the precipitates, and which gives rise to a localised corrosion which is fairly severe.

This differentiation has been obtained purposely by restraining the shearing elfect during the drawing process.

Example VII This example shows particularly well the fineness of the distribution obtained according to the invention.

It is an alloy with 1% of iron. It has been prepared by casting and drawing at the press. FIG. 5 shows the fineness of distribution on a sample taken from the periph eral zone of the bar which Was subjected to an intense shearing during the drawing.

In such an alloy, the distribution of the precipitates of the compounds FeAl is ensured in such a way, that the distance between two neighbouring precipitates should not exceed 5 microns at any point, this distance being measured micrographically in any direction in the product under examination.

What we claim is:

1. A method for the manufacture of an alloy consisting essentially of aluminum and at least one added metal selected from the group consisting of iron and nickel, comprising: forming granules of aluminum and from 0.05 to 4% of said added metal; compacting said granules while hot to form a compacted mass; and extruding said compacted mass to produce a shearing effect in at least the portion thereof adjacent to the surface, the compacting of said granules and subsequent shearing effecting an even distribution and fine dispersion of said added metal in the crystalline network of the aluminum, whereby the sheared portion of the extruded mass exhibits improved resistance to corrosion by water at high temperatures.

2. The method claimed in claim 1 in which said granules are of uniform composition.

3. The method claimed in claim 1 in which said granules are formed by melting aluminum together with said added metal, spraying the molten metal in the form of small droplets and solidifying said droplets.

4. The method claimed in claim 1 in which said granules are formed by coating aluminum granules with said added metal and heating them to cause diffusion of said added metal into the aluminum.

5. The method claimed in claim 1 in which said granules are formed by coating aluminum granules with a compound of said added metal reduceable by aluminum and heating said coated aluminum granules to reduce said compound and diffuse said added metal into the aluminum.

6. The method claimed in claim 1 in which said granules have a grain size of less than 300g.

7. The method of claim 4 in which said added metal is in finely powdered form.

8. A method for the manufacture of an alloy consisting essentially of aluminum and at least one added metal selected from the group consisting of iron and nickel, comprising: forming granules of aluminum and from 0.05 to 4% of said added metal; compacting said granules while hot to form a compacted mass; and extruding said compacted mass while subjecting it throughout its entire mass to a shearing action to effect an even distribution and fine dispersion of said added metal throughout the alloy mass, whereby said alloy exhibits improved resistance to corrosion by water at high temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 1,924,725 Rowe Aug. 29, 1933 2,170,039 Steudel Aug. 22, 1939 FOREIGN PATENTS 515,490 Italy Feb. 15, 1955 OTHER REFERENCES Metallurgical Abstracts, vol. 19, 1951-1952, p. 293, article titled The Sintering of Aluminum Alloys (original in Z. Metallkunde 1950, 41, (87, 228-231)).

Z. Metallukunde, 1950, 41, (8) 228-231. 

1. A METHOD FOR THE MANUFACTURE OF AN ALLOY CONSISTING ESSENTIALLY OF ALUMINUM AND AT LEAST ONE ADDED METAL SELECTED FROM THE GROUP CONSISTING OF IRON AND NICKEL, COMPRISING: FORMING GRANULES OF ALUMINUM AND FROM COMPRISISNG: FORMING GRANULES OF ALUMINUM AND FROM 0.05 TO 4% OF SAID ADDED METAL; COMPACTING SAID GRANULES 0.05 TO 4% OF SAID ADDED METAL, COMPACTING SAID GRANULES WHILE HOT TO FORM A COMPACTED MASS, AND EXTRUDING SAID WHILE HOT TO FORM A COMPACTED MASS; AND EXTURDING SAID COMPACTED MASS TO PRODUCE A SHEARING EFFECT IN AT LEAST THE PORTION THEREOF ADJACENT TO THE SURFACE, THE COMPACTING THR PORTION THEREOF ADJACENT TO THE SURFACE, THE COMPACTING OF SAID GRANULES AND SUBSEQUENT SHEARING EFFECTING AN EVEN DISTRIBUTION AND FINE DISPERSION OF SAID ADDED METAL IN THE CRYSTALLINE NETWORK OF THE ALUMIUNI, WHEREBY THE SHEARED CRYSTALLINE NETWORK OF THE ALUMINUM, WHEREBY THE SHEARED PORTION OF THE EXTRUDED MASS EXHIBITS IMPROVED RESISTANCE PORTION OF THE EXTRUDED MASS EXHIBIT IMPROVED RESISTANCE TO CORROSION BY WATER AT HIGH TEMPERATURES. 